Iran's military took part in defensive drills across the country on the same day the US imposed tough sanctions on the country.

The military exercises were part of joint drills involving the Iranian army and the Islamic Revolutionary Guard Corps, according to the Deputy Coordinator of Iranian Army.

The drills come as US President Donald Trump’s “toughest ever” sanctions hit Iran and are reportedly taking place in a 500,000 square kilometre area are expected to last until Tuesday.

Habibollah Sayyari, Deputy Coordinator of Iranian Army said: "I declare the codename for the beginning of this joint air defence drills - Velayat 97, of Islamic Republic of Iran's military and Islamic Revolutionary Guard Corps.”

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President of the US Donald Trump said Iran is struggling already due to his administration’s “very tough” policies.

He said: “We’ll see what happens with Iran, but they’re not doing very well, I can tell you.”

Iranian leader Hassan Rouhani vowed to disobey the sanctions and his country would continue to sell oil.

He said: "America wanted to cut to zero Iran's oil sales but we will continue to sell our oil to break sanctions.”

We’ll see what happens with Iran, but they’re not doing very well, I can tell you

Donald Trump

He added: "I announce that we will proudly bypass your illegal, unjust sanctions because it's against international regulations.

“We are in a situation of economic war, confronting a bullying power.

“I don't think that in the history of America, someone has entered the White House who is so against law and international conventions.”

World War 3: Iran's military took part in exercises on Monday (Image: RUPTLY•GETTY)

US Secretary of State, Mike Pompeo, told Fox News on Sunday: "We are working diligently to make sure we support the Iranian people and that we direct our activity towards ensuring that the Islamic Republic of Iran's malign behaviour is changed.

"That's the goal, that's the mission, and that's what we will achieve on behalf of the president."

More than 100 companies have pulled their business from Iran due to the further sanctions.

Thousands of protesters chanted "death to America" on the eve of the sanctions, which target the Middle Eastern country's vital energy and banking sectors.

The US withdrew from the Iran nuclear deal which was drawn up by the Obama administration and was agreed to by the UK, Russia, France, China, Germany and the EU.